Semiconductor memory device and method of manufacturing the same

ABSTRACT

A semiconductor memory device according to an embodiment comprises: a semiconductor substrate; a stacked body having a plurality of first insulating layers and conductive layers stacked alternately on the semiconductor substrate; a columnar semiconductor layer contacting the semiconductor substrate in the stacked body being provided extending in a stacking direction of the stacked body and including a first portion and a second portion which is provided above the first portion; a memory layer provided on a side surface of the columnar semiconductor layer facing the stacked conductive layers and extending along the columnar semiconductor layer; and a second insulating layer provided between one of the first insulating layer and the conductive layers of the stacked body. The columnar semiconductor layer has a boundary of the first portion and the second portion, the boundary being close to the second insulating layer; and an average value of an outer diameter of the memory layer facing a side surface of the second insulating layer is larger than that of of the memory layer facing a side surface of a lowermost layer of the first insulating layers in the second portion.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromUS Provisional Patent Application No. 62/311,546, filed on Mar. 22,2016, the entire contents of which are incorporated herein by reference.

FIELD

An embodiment described herein generally relates to a semiconductormemory device and a method of manufacturing the same.

BACKGROUND

A flash memory that stores data by accumulating a charge in a chargeaccumulation layer or floating gate, is known. Such a flash memory isconnected by a variety of systems, such as NAND type or NOR type, andconfigures a semiconductor memory device. In recent years, increasing ofcapacity and raising of integration level of such a semiconductor memorydevice have been proceeding. Moreover, a semiconductor memory device inwhich memory cells are disposed three-dimensionally (a three-dimensionaltype semiconductor memory device) has been proposed to achieve increasedcapacity and raised integration level of the semiconductor memorydevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram showing a schematic configurationof a semiconductor memory device according to a first embodiment.

FIG. 2 is an equivalent circuit diagram showing a configuration of amemory cell array 1 of the same semiconductor memory device.

FIG. 3 is a perspective view showing a configuration of the memory cellarray 1 of the same semiconductor memory device.

FIG. 4 is a schematic perspective cross-sectional view showing anexample of configuration of one memory cell MC included in the samesemiconductor memory device.

FIG. 5 is a plan view showing a configuration of part of the memory cellarray 1 included in the same semiconductor memory device.

FIGS. 6 and 7 are schematic cross-sectional view showing configurationsof the same semiconductor memory device.

FIGS. 8 to 13 are schematic cross-sectional views showing a method ofmanufacturing the same semiconductor memory device.

FIG. 14 is a schematic cross-sectional view showing a configuration of asemiconductor memory device according to a modified example.

FIG. 15 is a schematic cross-sectional view showing a comparativeexample.

DETAILED DESCRIPTION

A semiconductor memory device according to an embodiment comprises: asemiconductor substrate; a stacked body having a plurality of firstinsulating layers and conductive layers stacked alternately on thesemiconductor substrate; a columnar semiconductor layer contacting thesemiconductor substrate in the stacked body being provided extending ina stacking direction of the stacked body and including a first portionand a second portion which is provided above the first portion; a memorylayer provided on a side surface of the columnar semiconductor layerfacing the stacked conductive layers and extending along the columnarsemiconductor layer; and a second insulating layer provided between oneof the first insulating layer and the conductive layers of the stackedbody. The columnar semiconductor layer has a boundary of the firstportion and the second portion, the boundary being close to the secondinsulating layer; and an average value of an outer diameter of thememory layer facing a side surface of the second insulating layer islarger than that of the memory layer facing a side surface of alowermost layer of the first insulating layers in the second portion.

First Embodiment CONFIGURATION

Next, a semiconductor memory device according to an embodiment will bedescribed in detail with reference to the drawings. Note that thisembodiment is merely an example. For example, each of the drawings ofthe semiconductor memory device employed in the embodiment below isschematic, and thicknesses, widths, ratios, and so on, of layers are notnecessarily identical to those of the actual semiconductor memorydevice.

Moreover, the embodiment below relates to a semiconductor memory devicehaving a structure in which a plurality of MONOS(Metal-Oxide-Nitride-Oxide-Semiconductor) type memory cells(transistors) are stacked along a direction intersecting a surface of asubstrate (a Z direction in the drawings referred to hereafter), on thesubstrate, each of the MONOS type memory cells including: asemiconductor film acting as a channel provided in a column shape in theZ direction; and a gate electrode film provided, via a chargeaccumulation layer, on a side surface of the semiconductor film.However, the memory cell may be a memory cell of another form, forexample, a SONOS (Semiconductor-Oxide-Nitride-Oxide-Semiconductor) typememory cell or MANOS (Metal-Aluminum Oxide-Nitride-Oxide-Semiconductor)type memory cell, or a floating gate type memory cell.

FIG. 1 is a functional block diagram showing a configuration of asemiconductor memory device according to a first embodiment. Thesemiconductor memory device according to the embodiment comprises: amemory cell array 1; row decoders 2 and 3; a sense amplifier 4; a columndecoder 5; and a control signal generating unit 6. The memory cell array1 includes a plurality of memory blocks MB. Each of the memory blocks MBincludes a plurality of memory cells MC (not illustrated; mentionedlater in FIG. 3) arranged three-dimensionally therein. The row decoders2 and 3 decode a downloaded block address signal, and so on, and controla write operation and a read operation of data of the memory cell array1. The sense amplifier 4 detects and amplifies an electrical signalflowing in the memory cell array 1 during the read operation. The columndecoder 5 decodes a column address signal and controls the senseamplifier 4. The control signal generating unit 6, in addition toboosting a reference voltage and generating a voltage employed duringwrite, erase or the read operations, generates a control signal andcontrols the row decoders 2 and 3, the sense amplifier 4, and the columndecoder 5.

FIG. 2 is an equivalent circuit diagram showing a configuration of partof the memory cell array 1 according to the present embodiment.

The memory cell array 1 according to the present embodiment comprisesthe plurality of memory blocks MB. Moreover, a plurality of bit lines BLand a source line SL are commonly connected to these plurality of memoryblocks MB. Each of the memory blocks MB is connected to the senseamplifier via the bit line BL and to an unillustrated source line drivervia the source line SL.

The memory block MB comprises a plurality of memory units MU each havingits one end connected to the bit line BL and having its other endconnected, via a source contact LI, to the source line SL.

The memory unit MU comprises a plurality of the memory cells MCconnected in series. As will be mentioned later, the memory cell MCcomprises: a semiconductor layer; a charge accumulation layer; and acontrol gate. In addition, during various operations, a charge isaccumulated in the charge accumulation layer (write operation),moreover, a charge is erased from the charge accumulation layer (eraseoperation), based on a voltage applied to the control gate, whereby athreshold value of the memory cell MC is changed. Data stored in thememory cell MC is determined (read operation) by detecting a magnitudeof this threshold value. Note that hereafter, the plurality of memorycells MC connected in series will be called a “memory string MS”.

Commonly connected to the control gates of pluralities of the memorycells MC configuring different memory strings MS are, respectively, wordlines WL. These pluralities of memory cells MC are connected to the rowdecoder via the word lines WL.

The memory unit MU comprises a drain side select gate transistor STDconnected between the memory string MS and the bit line BL. Connected toa control gate of the drain side select gate transistor STD is a drainside select gate line SGD. The drain side select gate line SGD isconnected to the row decoder and selectively connects the memory stringMS and the bit line BL based on an inputted signal.

The memory unit MU comprises a source side select gate transistor STSconnected between the memory string MS and the source contact LI.Connected to a control gate of the source side select gate transistorSTS is a source side select gate line SGS. The source side select gateline SGS is connected to the row decoder and selectively connects thememory string MS and the source line SL based on an inputted signal.

FIG. 3 is a schematic perspective view showing a configuration of partof the memory cell array 1. Note that in FIG. 3, in order to explainmainly a principal portion of the memory cell array 1, such as aconductive layer, part of the configuration, such as an insulatinglayer, is omitted.

The memory cell array 1 according to the present embodiment comprises: asubstrate 101; and a plurality of conductive layers 102 stacked in the Zdirection, via an unillustrated inter-layer insulating layer, on thesubstrate 101. In addition, the memory cell array 1 includes a pluralityof memory columnar bodies 105 extending in the Z direction. Anintersection of the conductive layer 102 and the memory columnar body105 functions as the source side select gate transistor STS, the memorycell MC, or the drain side select gate transistor STD. The conductivelayer 102 is configured from a conductive layer of the likes of tungsten(W) or polysilicon, for example, and functions as the word line WL, thesource side select gate line SGS, and the drain side select gate lineSGD.

A conductive layer 106 functioning as the bit line BL and a conductivelayer 107 functioning as the source line SL are disposed above theconductive layer 102.

The memory cell array 1 comprises a conductive layer 108 that faces sidesurfaces in a Y direction of the plurality of conductive layers 102 andextends in an X direction. A lower surface of the conductive layer 108contacts the substrate 101. The conductive layer 108 is configured froma conductive layer of the likes of tungsten (W), for example, andfunctions as the source contact LI.

The plurality of conductive layers 102 are formed in a stepped shape attheir ends in the X direction and configure a stepped part 12.

A contact part 102 a is formed at an extremity of each step configuringthe stepped part 12. A contact 109 is disposed in the contact part 102a. The contact 109 is connected to an upper wiring line 110. Moreover,the stepped part 12 may comprise a support column 111 extending in the Zdirection to penetrate a stepped structure 12. The support column 111functions to maintain a posture of a stacked structure of the memorycell array 1 in a later-described step of replacing a sacrifice layerwith a conductive layer. To simplify explanation, only one supportcolumn 111 is shown, but a plurality of support columns 111 may beprovided.

FIG. 4 is a schematic perspective view showing a configuration of thememory cell MC. Note that FIG. 4 shows the configuration of the memorycell MC, but the source side select gate transistor STS and the drainside select gate transistor STD may also be configured similarly to thememory cell MC. Moreover, in FIG. 4, in order to explain mainly aprincipal configuration of the memory cell MC, such as a conductivelayer, a memory layer, or a semiconductor layer, part of theconfiguration, such as an insulating layer disposed above/below theconductive layer 102 or a barrier metal layer, is omitted.

The memory cell MC is provided so as to extend in the Z direction, at anintersection of the conductive layer 102 and the memory columnar body105. The memory columnar body 105 comprises: a core insulating layer121; and a semiconductor layer 122. The semiconductor layer 122 covers asidewall of the core insulating layer 121. A memory film 126 is providedon a side surface of the semiconductor layer 122. The memory film 126includes: a tunnel insulating layer 123 provided on the side surface ofthe semiconductor layer 122; a charge accumulation layer 124 provided ona side surface of the tunnel insulating layer 123; and a blockinsulating layer 125 provided on a side surface of the chargeaccumulation layer 124. Moreover, the conductive layer 102 is providedin a periphery of the block insulating layer 125.

The core insulating layer 121 is configured from an insulating layer ofthe likes of silicon oxide, for example. The semiconductor layer 122 isconfigured from a semiconductor layer of the likes of polysilicon, forexample. Moreover, the semiconductor layer 122 functions as a channelbody of the memory cell MC, the source side select gate transistor STS,and the drain side select gate transistor STD. The tunnel insulatinglayer 123 is configured from an insulating layer of the likes of siliconoxide, for example. The charge accumulation layer 124 is configured froman insulating layer capable of accumulating a charge, of the likes ofsilicon nitride, for example. The block insulating layer 125 isconfigured from, for example, silicon oxide or from a metal oxide suchas hafnium oxide, aluminum oxide, zirconium oxide, titanium oxide, ortantalum oxide whose permittivity is higher than that of silicon oxide,or from a stacked body of these.

Next, a configuration of the semiconductor memory device according tothe present embodiment will be described in more detail with referenceto FIGS. 5 to 7.

As shown in FIG. 5, in the present embodiment, the memory columnarbodies 105 are arranged staggered. In addition, the source contact LI isformed in a striped shape having the X direction as its longitudinaldirection. This source contact LI is implanted, via an inter-layerinsulating film 127, in a trench Ta that divides the memory cell array 1in a block unit.

As shown in FIG. 6, in the present embodiment, the above-describedmemory columnar body 105 is provided on the semiconductor substrate 101.The memory film 126 is provided on a side surface of the memory columnarbody 105.

The memory columnar body 105 and the memory film 126 include a firstportion P1 and a second portion P2. A lower end of the first portion P1is connected to the semiconductor substrate 101. A lower end of thesecond portion P2 is connected to an upper end of the first portion P1.

Moreover, as shown in FIG. 7, a central axis CA1 of the first portion P1and a central axis CA2 of the second portion P2 are in differentpositions in the Y direction. In other words, the two central axes CA1and CA2 never form an identical straight line in the Y-Z plane shown inFIG. 7. Now, the central axis CA1 of the first portion P1 or centralaxis CA2 of the second portion P2 represents a line passing through thecenter in an X-Y cross section, in the first portion P1 or secondportion P2, of the memory columnar body 105 and the memory film 126.Note that the “center” of the above-described central axis refers to thecenter of the memory columnar body 105 or the memory film 126 in thecase where a certain degree of processing variation or distortion ofshape are ignored and where the first portion P1 and second portion P2are regarded as being on the whole column shaped, and are regarded asbeing substantially circular shaped in an X-Y cross-section. Moreover,the “axis” is a line passing through the above-described “center”, andis not necessarily limited to extending in the Z direction (beingperpendicular to the surface of the substrate 101).

In FIG. 7, the two central axes CA1 and CA2 are misaligned in the Ydirection, but they may further be misaligned also in the X direction.Moreover, they may be misaligned in either one of the X direction or theY direction.

A plurality of the conductive layers 102 are stacked in the Z direction,via an inter-layer insulating layer 103, in a periphery of the memoryfilm 126.

In the present embodiment, an insulating layer 112 is provided betweenan uppermost layer of the inter-layer insulating layer 103 t provided ona side surface of the first portion P1 and a lowermost layer of theconductive layer 102 b provided on a side surface of the second portionP2, at a boundary of the first portion P1 and the second portion P2 ofthe memory columnar body 105 and the memory film 126. In other words,the boundary of the first portion P1 and the second portion P2 of thememory columnar body 105 and the memory film 126 is close to theinsulating layer 112.

Moreover, an average value W2 of an outer diameter of the memory film126 of a portion where the insulating layer 112 is provided is largerthan an average value W1 of an outer diameter of the memory film 126 ofa portion facing a lowermost layer of the inter-layer insulating layer103 b of the second portion P2. Furthermore, outer diameters of thememory layer 126 and the memory columnar body 105 facing the insulatinglayer 112 increase in a downward Z direction. Now, the average value W1or W2 of the outer diameter refers to an average value of the outerdiameter in an X-Y cross section, of the memory film 126 of a portionfacing the inter-layer insulating layer 103 b or the memory film 126 ofa portion where the insulating layer 112 is provided. Moreover, thememory film 126 has the configuration shown in FIG. 4. Therefore, theouter diameter of the memory film 126 means an outer diameter of theblock insulating layer 125 in the present embodiment.

Now, the case where the insulating layer 112 is not provided will bedescribed using a comparative example of FIG. 15. In this comparativeexample, a portion (portion surrounded by the dotted line A) close tothe boundary of the first portion P1 and the second portion P2 does nothave the insulating layer 112 disposed therein, hence outer diameters ofa memory film 126′ and a semiconductor layer 122′ of a memory columnarbody 105′ decrease sharply in a downward Z direction, and thesemiconductor layer 122′ of the portion close to the boundary is thinnedmore than another portion. In other words, the semiconductor layer 122′forms a current channel of each of the memory cells, but in the portionclose to the boundary, a width of the semiconductor layer 122′ isreduced, whereby resistance of the current channel ends up rising.

On the other hand, in the present embodiment, the insulating layer 112is provided close to the boundary of the first portion P1 and the secondportion P2, hence a distance between the uppermost layer of theconductive layer 102 t (uppermost layer of the memory cell MC) facingthe first portion P1 and the lowermost layer of the conductive layer 102b (lowermost layer of the memory cell MC) facing the second portion P2ends up being separated. Furthermore, the outer diameters of the memoryfilm 126 and the semiconductor layer 122 of the memory columnar body 105facing the insulating layer 112 increase gently in a downward Zdirection. In other words, there is a structure in which although thewidth of the semiconductor layer 122 narrows toward the portion close tothe boundary, narrowing of the width is relieved in proportion to a filmthickness of the insulating layer 112, and from there on there is abroadening of the width to a certain depth.

As a result, a rise in resistance of the semiconductor layer 122 actingas a current channel, accompanying the decrease in diameter in an X-Ycross section of the semiconductor layer 122 at the boundary of thefirst portion P1 and the second portion P2, of the memory columnar body105, is suppressed. In other words, it becomes possible to preventdeterioration of current characteristics and to maintain good cellcharacteristics.

Moreover, in the present embodiment, an inner side surface of theinsulating layer 112 has a gentle curved shape. As a result, even whenthe central axis of the first portion P1 and the central axis of thesecond portion P2 are misaligned, misalignment of the central axes canbe smoothly connected, hence a film thickness of the memory film 126provided on the inner side surface of the insulating layer 112 can bekept uniform. Therefore, it also becomes possible to suppressdeterioration of withstand voltage of the memory film 126 due to thefilm thickness of the memory film 126 varying, and to improvereliability of the memory cell.

Note that the inter-layer insulating layer 103 is configured from aninsulating material of the likes of silicon oxide, for example. Theinsulating layer 112 is configured from an insulating material of thelikes of silicon oxide, for example. Now, as a condition for selecting amaterial of the insulating layer 112, the insulating layer 112 ispreferably of a material whose etching rate with respect to etchingperformed in a later-described method of manufacturing is higher thanthat of the inter-layer insulating layer 103. These materials, etchingconditions, and so on, will be described later.

METHOD OF MANUFACTURING

The method of manufacturing according to the present embodiment will bedescribed using FIGS. 8 to 13.

As shown in FIG. 8, a plurality of the inter-layer insulating layers 103and sacrifice layers 104 are stacked alternately on the semiconductorsubstrate 101. In this way, a first stacked body LB1 corresponding tothe first portion P1 is formed. The sacrifice layer 104 is configuredfrom silicon nitride, for example. Moreover, in the present embodiment,the inter-layer insulating layer 103 is configured from silicon oxideusing a CVD method.

As shown in FIG. 9, patterning of a desired pattern corresponding to amemory hole MH is performed by lithography, and a first hole Ho1 isformed by RIE or wet etching.

As shown in FIG. 10, a sacrifice layer 113 is formed by using adeposition method such as CVD in the first hole Ho1. Note that otherlayers and films described below could be formed similarly. In thepresent embodiment, the sacrifice layer 113 is configured from silicon.Alternatively, it is also possible to employ a stacked body configuredfrom titanium nitride and tungsten sequentially formed from an innersidewall of the hole Ho1.

As shown in FIG. 11, the insulating layer 112 is formed on the firststacked body LB1, and a plurality of the inter-layer insulating layers103 and sacrifice layers 104 are stacked alternately on the insulatinglayer 112. In this way, a second stacked body LB2 corresponding to thesecond portion P2 is formed.

Now, as mentioned above, the insulating layer 112 is configured from amaterial whose etching rate in a certain etching method is higher thanthat of the inter-layer insulating layer 103. Specifically, theinsulating layer 112 is configured from a material having a higheretching rate than the inter-layer insulating layer 103 during etchingemployed during removal of the sacrifice layer 113, which will bedescribed below. In the present embodiment, the inter-layer insulatinglayer 103 is configured from silicon oxide using a plasma CVD method. Inthis case, during removal of the sacrifice layer 113, wet etchingemploying a dilute hydrofluoric acid (dHF) solution, for example, isperformed. Moreover, the insulating layer 112 is configured from amaterial whose etching rate with respect to the dilute hydrofluoric acidsolution is higher than that of the silicon oxide configuring theinter-layer insulating layer 103. Specifically, the insulating layer 112is configured from silicon oxide formed using a plasma CVD method, inthe same way as the inter-layer insulating layer 103, for example.However, formation conditions of the inter-layer insulating layer 103and the insulating layer 112 are made different. Specifically, forexample, a formation condition of the inter-layer insulating layer 103is set to being performed under an atmosphere of about 300° C., and aformation condition of the insulating layer 112 is set to beingperformed under an atmosphere of about 200° C. which is morelow-temperature than the formation condition of the inter-layerinsulating layer 103. As a result, a large amount of impurities is mixedinto the insulating layer 112, and Si—OH bonds or Si—H bonds increase,whereby the number of Si—O bonds decreases. In other words, theinsulating layer 112 attains a state where oxygen is more deficient thanin a stoichiometry state, and its density decreases. As a result, theinsulating layer 112 becomes more easily etched than the inter-layerinsulating layer 103.

Now, a film thickness of the inter-layer insulating layer 103 is set toabout 35 nm, for example. In this case, a combined film thickness of theinsulating layer 112 and the uppermost layer of the inter-layerinsulating layer 103 t of the first stacked body LB1 is preferably about70 nm or less from a viewpoint of suppressing channel resistance.

However, the combined film thickness of the insulating layer 112 and theinter-layer insulating layer 103 t may be set to about the same as afilm thickness of another inter-layer insulating layer 103. This makesit possible to suppress an increase in oxide film thickness close to theboundary of the first portion P1 and the second portion. P2. Therefore,increase in channel resistance is suppressed.

A film thickness of the insulating layer 112 may be about the same asthe film thickness of another inter-layer insulating layer 103.Therefore, for example, the film thickness of the inter-layer insulatinglayer 103 t and the film thickness of the insulating layer 112 may eachbe set to about 35 nm. The film thickness of the insulating layer 112 isof course not limited to this, and may be 20 to 50 nm, for example.

However, the film thickness of the insulating layer 112 may be madegreater than that of the inter-layer insulating layer 103 t. As aresult, a level difference close to the boundary of the first portion P1and the second portion P2 during later memory hole MH formation can bemade gentle, and formation of the memory film 126 can be performedfavorably.

As shown in FIG. 12, patterning of a desired pattern corresponding tothe memory hole MH is performed by lithography, and a second hole Ho2 isformed by RIE or wet etching, similarly to in FIG. 9.

As shown in FIG. 13, the sacrifice layer 113 is selectively removed bywet etching using a dilute hydrofluoric acid solution. At this time, asmentioned above, a film quality of the insulating layer 112 is lessdense than that of the inter-layer insulating layer 103, hence etchingof the insulating layer 112 proceeds relatively more quickly thanetching of the inter-layer insulating layer 103, and an inner diameterof the inner sidewall of the insulating layer 112 increases in adownward Z direction. In this way, the memory hole MH is formed.

Then, the memory film 126 and the memory columnar body 105 are formedsequentially on an inner wall of the memory hole MH, whereby theconfiguration of FIG. 6 is obtained.

Now, in the step of forming the memory film 126 and the memory columnarbody 105 on the inner wall of the memory hole MH, it is required that,after formation of the memory film 126, in order to connect thesubstrate 101 or a layer epitaxially grown thereon to the later-formedsemiconductor layer 122, part of the memory film 126 in a memory hole MHbottom part is removed by etching, and a substrate 101 surface isexposed.

However, there is a risk that if the memory hole MH is formed dividedinto a lower layer memory hole (first hole Ho1) and an upper layermemory hole (second hole Ho2), then when a position of the second holeHo2 is misaligned in the XY directions with respect to a central axisdirection of the first hole Ho1, an opening of the portion close to theboundary becomes small, and sufficient RIE cannot be performed.

On the other hand, by forming the insulating layer 112 from a materialmore easily etched than that of the inter-layer insulating layer 103 asin the present embodiment, the opening of the portion close to theboundary of the first hole Ho1 and the second hole Ho2 can be madelarger, and RIE can be performed favorably to the memory hole MH bottompart. Moreover, since there is no need for the memory film 126 to befilm thinned to broaden the opening, memory characteristics are neverdegraded by film thinning.

MODIFIED EXAMPLE

As shown in FIG. 14, there may be a configuration in which theconductive layer 102 t, not the inter-layer insulating layer 103 t, isadopted as a layer below the insulating layer 112. By doing so, a filmthickness of silicon oxide between the first portion P1 and the secondportion P2 of the memory film 126 and the memory columnar body 105 isthinned, and a voltage applied to the conductive layer 102 (word lineWL) to invert the semiconductor layer 122 can be reduced.

OTHERS

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms: furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

1. A semiconductor memory device, comprising: a semiconductor substrate;a stacked body having a plurality of first insulating layers andconductive layers stacked alternately on the semiconductor substrate; acolumnar semiconductor layer being provided above the semiconductorsubstrate in the stacked body, being provided extending in a stackingdirection of the stacked body and including a first portion and a secondportion which is provided above the first portion; a memory layerprovided on a side surface of the columnar semiconductor layer facingthe stacked conductive layers and extending along the columnarsemiconductor layer; and a second insulating layer provided between oneof the first insulating layers of the stacked body and the conductivelayer, the columnar semiconductor layer having a boundary of the firstportion and the second portion, the boundary being close to the secondinsulating layer, an average value of an outer diameter of the memorylayer facing a side surface of the second insulating layer being largerthan that of the memory layer facing a side surface of a lowermost layerof the first insulating layers in the second portion, and a diameter ofan inner sidewall of the second insulating layer facing a side surfaceof the memory layer increasing downwardly.
 2. The semiconductor memorydevice according to claim 1, wherein a central axis passing through acenter of a cross section parallel to a surface of the substrate, of thefirst portion, and a central axis passing through a center of a crosssection parallel to the surface of the substrate, of the second portionare in different positions in a direction parallel to the surface of thesubstrate.
 3. The semiconductor memory device according to claim 1,wherein the first insulating layer includes silicon and oxygen, and thesecond insulating layer includes silicon and oxygen, and has an etchingrate with respect to a hydrofluoric acid solution higher than that ofthe first insulating layer.
 4. The semiconductor memory device accordingto claim 1, wherein a film thickness of the second insulating layer issubstantially identical to that of the first insulating layer.
 5. Thesemiconductor memory device according to claim 1, wherein a total of afilm thickness of the first insulating layer and a film thickness of thesecond insulating layer is 70 nm or less.
 6. (canceled).
 7. A method ofmanufacturing a semiconductor memory device, comprising: alternatelystacking a plurality of first insulating layers and first layers on asemiconductor substrate, thereby forming a first stacked body; forming afirst hole penetrating the plurality of first insulating layers and theplurality of first layers; forming a first sacrifice layer in the firsthole; forming a second insulating layer on the first stacked body, andalternately stacking a plurality of the first insulating layers and thefirst layers on the second insulating layer, thereby forming a secondstacked body; forming a second hole penetrating the second stacked bodyand exposing an upper surface of the first sacrifice layer; removing thefirst sacrifice layer and an inner sidewall of the second insulatinglayer by etching via the second hole, thereby forming a third hole; andforming a memory film and a semiconductor layer on an inner wall of thethird hole.
 8. The method of manufacturing a semiconductor memory deviceaccording to claim 7, wherein the first sacrifice layer is formed usinga material that includes silicon.
 9. The method of manufacturing asemiconductor memory device according to claim 7, further comprisingduring the etching, employing a method of a kind where an etching rateof the second insulating layer will be higher than that of the firstinsulating layer.
 10. The method of manufacturing a semiconductor memorydevice according to claim 7, wherein the first insulating layer andsecond insulating layer are silicon oxide layers formed using a plasmaCVD (Chemical Vapor Deposition) method.
 11. The method of manufacturinga semiconductor memory device according to claim 10, wherein the plasmaCVD forming the second insulating layer is performed under an atmosphereof 200° C. or less.
 12. The method of manufacturing a semiconductormemory device according to claim 10, wherein the etching is wet etchingemploying a dilute hydrofluoric acid solution.
 13. The semiconductormemory device according to claim 1, wherein the diameter of the secondinsulating layer is a diameter in the direction orthogonal to thestacking direction of the stacked body.
 14. The method of manufacturinga semiconductor memory device according to claim 7, wherein the innersidewall of the second insulating layer is removed to increase an innerdiameter of the second insulating layer downwardly.
 15. The method ofmanufacturing a semiconductor memory device according to claim 14,wherein the inner diameter of the second insulating layer is a diameterin a direction orthogonal to a stacking direction of the first andsecond stacked body.